1. Field of the Invention
The invention relates to a motor structure and, more particularly, to a motor having a magnetic bearing using magnetic forces to avoid rotation friction.
2. Description of the Related Art
Referring to the prior fan motor structure shown in FIGS. 1 and 2, the structure includes a base 12, a stator 13, a rotor 14 and a bearing 15.
Referring to FIG. 1, the base 12 is located in the center of a fan frame 201 and the base 12 and the fan frame 201 are integrally formed together. A bearing seat 21 is located in the center of the base 12. An accommodation portion 31 is provided in the center of the stator 13. Outside the accommodation portion 31 are a coil 32 and a piece of silicon steel 33, with a circuit board 34 underneath. The coil 32, the silicon steel 33 and the circuit board 34 are electrically connected. The accommodation portion 31 is telescoped to the outer surface of the bearing seat 21 of the base 12.
Referring to FIG. 2, the rotor 14 includes a hollow cylinder 44 that has an open end. A set of fan blades 43 are attached to the outer wall of the hollow cylinder 44 while a ring-shaped magnet 41 is allocated at its inner wall. A rotation shaft 42 is provided at the center of the ring-shaped magnet 41 and is accommodated in the bearing 15. When the coil 32 of the stator 13 is electrically excited, the rotor 14 is able to rotate relatively to the stator 13 due to the magnetic forces.
The bearing 15 is a self-lubricating bearing fixed onto the bearing seat 21 of the base 12. It accommodates the rotation shaft 42 of the rotor 14.
The elastic washer 7 is telescoped on the upper part of the rotation shaft 42 to act as an elastic buffer between the rotor 14 and the bearing 15.
The C-ring 16 is jointed with a groove 133 situated near the lower end of the rotation shaft 42 to prevent the rotor 14 from disengaging from the base 12.
It is observed from the above structure that, in prior structures, the C-ring 16 is employed to axially position the rotation shaft 42 of the rotor 14. To describe at length, when the rotor 14 rotates due to the electric excitation of the coil 32, the wind force F1 acts downwards towards the bottom of the base 12, and as a result of the counterforce F2, the rotor 14 disengages from the base 12. Therefore, the presence of the C-ring 16 prohibits the rotor 14 from disengaging from the base 12.
However, in the first prior technique, when the fan rotates, wear and heat due to friction occur between the C-ring 16 and the rotation shaft 42, thereby shortening the operational life span. Also, the friction between the C-ring 16 and the rotation shaft 42 generates noise, or unsteady rotation speed may occur depending on the degree of friction. Over the above description, the rotor 14 and the stator 30 are designed with magnetic bias therebetween. Therefore, when the rotor 14 rotates, magnetic levitation is created, resulting in magnetic equilibrium between the rotor 14 and the stator 30 at a stable position. However, during the rotation, the rotor 14 deviates the rotation shaft 42 consequent on the external forces, such as wind forces, it receives, in such a manner that the rotor 14 and the stator 30 are no longer in previous equilibrium positions, but are in new equilibrium positions depending on the degree of the received external forces. This gives rise to a comparatively great difficulty in the design.